This invention relates to a method of and apparatus for fabrication of an insulated fluid storage unit and particularly a hot water unit, and in particular to a tank type hot water heater unit having an outer insulation within an outer shell.
Hot water heaters for domestic and other applications generally include an inner storage tank having an associated heating unit for heating of the water in the storage tank. The tank is enclosed within suitable insulation to retain the heat and minimize the necessity for frequent reheating. In other applications, a storage tank for cold or hot material or the like may be insulated to retain the heat or prevent heat from passing into the material. In a hot water heater unit, for example, an outer esthetically pleasing shell or housing may be provided to enclose the insulation, depending upon the application and usuage.
A highly satisfactory insulating material is an expandable insulation such as an expanded foamed polyurethane. The insulation can be applied in a fluid or semi-fluid state and foamed to produce a rigid and closely adhering insulating enclosure about the inner tank. U.S. Pat. No. 3,253,731, issued May 31, 1966, entitled "Hot Water Storage Tanks", discloses a hot water heater in which the storage tank is insulated with a foamed insulation.
The inventors copending application entitled "Insulated Fluid Storage Unit And Method Of Fabrication" which was filed on the date of this application discloses a particularly satisfactory polyurethane foam insulated hot water heater unit.
Water heaters are often provided with a gas burner aligned with the bottom of the storage tank for heating of the water within the storage tank. In gas fired units, a firing chamber is secured extending downwardly from the bottom of the storage tank, generally with encircling insulation about the gas firing chamber. Polyurethane, when burned, produces toxic fumes. As more fully discussed in the above patent, foamed polyurethane insulation must be protected from the direct temperature of the heating units.
In-situ application of the insulation to the tank therefore requires provision of appropriate confining wall means and various systems as discussed in the inventors above identified application. Generally, the outer shell is telescoped over the tank and sealing twice then located between the shell and tank to define the bottom cavity wall. An inflatable bag member may be inserted between a lower end of the shell and tank and inflated to form the bottom wall of the insulating cavity with the opposed walls of the tank and shell. The bag seals the cavity and foam insulation material is applied in a semi-liquid state with a foaming additive, causing the material to expand and fill all voids within the cavity. Typical systems for inserting a foamed insulation using an inflatable confining bag are shown for example in U.S. Pat. No. 4,372,028, issued Feb. 8, 1983, entitled "Method Of Manufacturing Foam Insulated Tank", and U.S. Pat. No. 4,477,399, issued Oct. 16, 1984, entitled "Method And Apparatus For Manufacturing A Foam Insulated Water Heater".
An alternative method of applying a foamed insulation uses an envelope inserted between the preassembled storage tank and outer shell. Foam insulation is introduced into the envelope and expands within the envelope to fill the voids therein and produces the insulating jacket about the tank. Envelope type structures are shown in U.S. Pat. No. 4,447,377, issued May 8, 1984, and entitled "Method Of Insulating The Exterior Of A Water Heater Tank "and U.S. Pat. No. 4,527,543, issued July 9, 1985, and entitled "Water Heater Construction" wherein a multilayer fiberglass belt is clamped about a tank to form the bottom wall of the insulation cavity.
In a commercial structure, the assignee of this application has built foam insulated hot water heaters using a flexible polyurethane dam member forming the bottom wall of the cavity. In the commercial system, a pair of heavy metal plates, each generally corresponding to half of the inner tank were provided. The half members were formed with curved configurations and domed upper ends. The heavy metal members were interconnected at the top of a suitable linkage and coupled to a power hoist mechanism for alignment with a heater tank. The interconnecting members were thus generally in the form of a clam-shell structure. The tank was formed with an encircling polyurethane belt which was adhesively bonded to the tank. Two workmen were provided and each moved one of the clam shells outwardly as the clam-shell unit was dropped downwardly over the tank by the hoist. The shells were released to drop onto and compress the polyurethane belt. The hoist was then disconnected from the clam and the shell rested on the tank. The hoist was removed, and rested over the tank to receive the outer heater shell, after which the hoist was returned and the heavy metal clam-shell unit removed, thereby establishing the cavity for receiving of the foam insulation.
The prior art foamed insulation systems for hot water heaters thus have been suggested and even used in commercial applications, the requirement of the special inflatable structures and/or envelope type devices require careful attention and application, and may materially add to the cost of the heater structure and the fabrication of the heater.